To obtain a polymer electrolyte fuel cell that generates electricity and heat simultaneously by electrochemically reacting a fuel gas and an oxidant gas, first, catalyst layers are formed on both surfaces of a polymer electrolyte membrane that selectively transports hydrogen ions using a mixture containing at least a carbon powder carrying an electrode catalyst (e.g., platinum metal catalyst) for accelerating an electrode reaction on an anode or a cathode, and a cation exchange resin (hydrogen ion conductive polymer electrolyte).
Then, on the outer surfaces of the catalyst layers are formed gas diffusion layers having both fuel gas permeability and electron conductivity. The catalyst layers are sometimes called gas diffusion electrodes. In some cases, the combination of a catalyst layer and a diffusion layer is called a gas diffusion electrode.
In order to prevent supplied fuel gas from leaking to the outside or to prevent the fuel gas and oxidant gas from mixing with each other, on the peripheries of the gas diffusion electrodes are placed gas sealants or gaskets, with the polymer electrolyte membrane between the gas diffusion electrodes. Such sealants or gaskets are combined with the gas diffusion electrodes and the polymer electrolyte membrane, forming a membrane electrode assembly (MEA). Alternatively, the combination of a polymer electrolyte membrane and the gas diffusion electrodes is called membrane electrode assembly (MEA).
On the outer surfaces of the MEA are disposed conductive separators for fixing adjacent MEAs to each other and electrically connecting the MEAs in series. On the surface of each separator to be in contact with the MEA is formed a gas channel for supplying a reaction gas to the electrode surface of the MEA and removing an electrode reaction product and excess gas to the outside of the MEA. The gas channel is usually formed by providing a groove on the separator surface, but it may be formed as a separate member.
Most polymer electrolyte fuel cells comprise a stack formed of a plurality of stacked unit cells, each unit cell comprising an MEA as described above and a pair of separators for sandwiching the MEA. Because heat is generated by the generation of power during operation, cooling water channels are formed between every one to three unit cells so as to maintain the cell temperature at a constant level. The generated thermal energy is utilized in the form of warm water or the like.
The gas diffusion electrodes and polymer electrolyte fuel cells as described above, however, had the following problem. Impurities such as organic substance entering into a fuel cell from the outside after its shutdown poison and degrade the catalyst in the MEA. As a result, the fuel cell cannot exert its original performance in subsequent operations, or the cell's durability decreases at an early stage of long-term power generation.
In view of this, for example, Patent Document 1 discloses a technique in which water is filled into the fuel or oxidant gas channel of a fuel cell before its shutdown and the fuel cell is preserved while the fuel or oxidant gas channel is filled with the water.
Patent Document 1: JP 6-251788 A